The present invention relates to a method and apparatus for economically ensuring the precise and reproducible automation of laboratory instrumentation. Particularly, the present invention relates to precision movement of laboratory instrumentation such as pipette tips in a manner that overcomes hysteresis inherent in gear-driven positioning mechanisms.
Automated laboratory handling systems require precise, repeatable movements to be made in a predictable manner, as the machinery used must meter out very small amounts of liquid and move within extremely small microplate wells with precision and accuracy. Laboratory pipetting systems, in particular, must be precisely controlled to move in the X, Y, and Z planes in order to position a bank of micropipette tips into the bottom of corresponding microplate wells. If a pipette tip is not inserted deeply enough into a well, a sufficient amount of the liquid may not be removed, potentially compromising the test or reaction. Further, if the pipette tip is inserted too deeply, damage could result to the pipette tip or delivery apparatus. Creating machinery with this type of predictability of movement is difficult due to the fact that numerous components comprising any mechanical system have a certain amount of imprecision in their fit with one another. When aggregated into a final assembly, an unpredictable amount of “play” in the final movement of the machinery occurs, often referred to as hysteresis. The presence of hysteresis indicates the inability to predict the exact location of a given component, which could result in broken instrumentation, reduced ability to uptake or adequately measure a given chemical in a chemical well, or contamination of a sample.
Reduction of hysteresis is often accomplished by utilizing highly precise components such as precision ground gears and precision servo motors, or by utilizing expensive position sensing systems. These methods leave much to be desired, as the components add substantial sums to the final cost of a system, and precision gears must be routinely replaced to account for the reduction in precision as friction takes its toll on the components. Further, although precision components are subject to a very small maximum value of error, the amount of error is not consistently the same. Therefore, these conventional methods of reducing hysteresis in mechanical devices result in high costs that do not necessarily guarantee precision or predictability.
Therefore, an efficient, reliable and low-cost hysteresis compensation device operable to reduce slop, play, or backlash associated with positioning laboratory equipment is desired.